/*Easy
Given a binary tree, find its maximum depth.

The maximum depth is the number of nodes along the longest path
from the root node down to the farthest leaf node.

Note: A leaf is a node with no children.

Example:
Given binary tree [3,9,20,null,null,15,7],

    3
   / \
  9  20
    /  \
   15   7
return its depth = 3. */

#include <algorithm>

using namespace std;

struct TreeNode {
    int val;
    TreeNode *left;
    TreeNode *right;
    TreeNode(int x) : val(x), left(NULL), right(NULL) {}
};

class Solution {
public:
    int maxDepth(TreeNode* root) {
        if (!root) {
            return 0;
        }

        return 1 + max(maxDepth(root->left), maxDepth(root->right));
    }
};